A broad-spectrum anti-fouling isolation fluid for cementing ultra-deep wells and its preparation method

Abstract

This invention relates to the field of oil and gas field drilling and cementing technology, and in particular to a broad-spectrum anti-fouling isolation fluid for ultra-deep well cementing and its preparation method, comprising the following components: a zwitterionic nanocomposite polymer, a composite flushing agent, a weighting agent, and water; the zwitterionic nanocomposite polymer is an organic-inorganic hybrid copolymer with surface-silanized modified nano-silica as an inorganic crosslinking core, and polymeric segments copolymerized and grafted onto the surface of the inorganic crosslinking core; the monomers of the polymeric segments include N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride, and isopentenyl polyoxyethylene ether; the composite flushing agent contains alkyl glycosides and alkyl sulfobetaine surfactants.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field drilling and cementing technology, and in particular to a broad-spectrum anti-contamination isolation fluid for cementing ultra-deep wells and its preparation method. Background Technology

[0002] As global oil and gas exploration and development strategies continue to extend into deep-earth resources, ultra-deep wells (typically referring to drilling projects with depths exceeding 8,000 meters) have become the core technological battleground for enhancing oil and gas recovery. In ultra-deep well cementing engineering, after casing is installed, a separator fluid must be used to effectively isolate and replace the drilling fluid (especially the widely used oil-based drilling fluid) with the subsequently pumped cement slurry. Through a surface-active mechanism, the wetting of the casing metal surface and the wellbore rock surface is reversed from "strongly oleophilic" to "strongly hydrophilic," thereby ensuring the bonding quality of the cement stone interface and the integrity of the interlayer seal.

[0003] However, in practical engineering applications, the bottom of ultra-deep wells faces extremely harsh environments with ultra-high temperatures (bottom-hole static temperatures typically exceed 220°C) and extremely high salinity. Existing conventional cementing and sealing fluids exhibit serious technical defects under these conditions, leading to the synergistic failure of hydrodynamic and interfacial chemical interactions. On the one hand, the thickeners and suspending stabilizers relied upon by conventional polymer sealing fluids are prone to severe thermo-oxidative degradation and agglomeration under the dual destruction of temperatures exceeding 200°C and the compression of the double electric layer by high-valence cations. This "thermodynamic thickening" phenomenon directly causes the sealing fluid to lose its suspending capacity, triggering gravity settling and density stratification of high-density weighting materials within the wellbore, which in turn leads to cross-linking and mixing of mud and cement slurry, or even catastrophic accidents such as blowouts and lost circulation. On the other hand, under ultra-high temperature conditions, the hydrophilic groups of surfactants in conventional flushing agents are prone to desorption or pyrolysis, resulting in a significant decrease in their interfacial activity and emulsification stripping ability, making it difficult to effectively strip dense oil films. More seriously, once the separator fluid is deeply contaminated by oil-based mud, the strong emulsifiers in the oil-based mud will undergo harmful interfacial chemical complexation reactions with the water-soluble polymers in the separator fluid, leading to irreversible flocculation and abnormal thickening of the fluid. The aforementioned physical suspension failure and chemical flushing failure couple under extreme conditions, resulting in a large amount of oil film remaining at the wellbore interface. The hydration products of the cement slurry cannot form effective chemical bonds, ultimately causing high-pressure fluid to leak outside the pipe, seriously threatening the long-term sealing integrity of the oil and gas well. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a broad-spectrum anti-fouling isolation fluid for cementing ultra-deep wells and its preparation method. This approach, by introducing a hybrid copolymer with a special topological structure in synergy with a composite flushing agent, effectively overcomes the rheological failure and oil-based mud contamination and flocculation problems under extreme high temperature and high salinity conditions, starting from the chemical bottom-level reaction kinetics and multi-level interfacial thermodynamic reconstruction.

[0005] According to one aspect of the present invention, a broad-spectrum anti-fouling isolation fluid for cementing ultra-deep wells is provided, comprising the following components: a zwitterionic nanocomposite polymer, a composite flushing agent, a weighting agent, and water. The zwitterionic nanocomposite polymer is an organic-inorganic hybrid copolymer with surface-silanized modified nano-silica as an inorganic crosslinking core, and polymeric segments copolymerized and grafted onto the surface of the inorganic crosslinking core; the monomers of the polymeric segments include N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride, and isopentenyl polyoxyethylene ether. The composite flushing agent comprises alkyl glycosides and alkyl sulfobetaine surfactants. The role of the above components is that the surface-silanized modified nano-silica acts as sparse physical cross-linking nodes, inducing the formation of star-shaped macromolecules with nanoparticles as the core. Its mechanical rigidity physically inhibits the complete collapse of the polymer chain at high temperatures. N,N-dimethylacrylamide provides a rigid framework resistant to hydrolysis; 2-acrylamido-2-methylpropanesulfonic acid provides strong anionic electrostatic repulsion to resist calcium and magnesium ion compression of the electric double layer; N-vinylpyrrolidone utilizes a five-membered lactam ring to increase chain segment rigidity; dimethyl diallyl ammonium chloride introduces cationic sites to form an amphoteric charge balance; and isopentenyl alcohol polyoxyethylene ether... As a thermosensitive macromolecular associative monomer, its polyoxyethylene segments exhibit hydrophilicity at room temperature by forming a stable hydration shell with water molecules through hydrogen bonds. When the temperature rises above its cloud point, the polyoxyethylene segments undergo intermolecular association after dehydration, constructing a dynamic and reversible physical cross-linking network to compensate for the degradation and thickening effect caused by high temperature. At the same time, alkyl glycosides provide high-temperature resistant nonionic rinsing ability, and alkyl sulfobetaine, with its zwitterionic head group and sulfonate structure, possesses excellent high-temperature resistance and resistance to calcium and magnesium ion precipitation. The two work together to achieve efficient oil film stripping and stable dispersion of water-in-oil nanoemulsions.

[0006] Preferably, based on 100 parts by weight of water, the amounts of each component are as follows: 2.0 to 4.0 parts by weight of the zwitterionic nanocomposite polymer, 1.5 to 2.5 parts by weight of the alkyl glycoside, 0.3 to 0.8 parts by weight of the alkyl sulfobetaine surfactant, and 50 to 300 parts by weight of the weighting agent. The polymer dosage is controlled between 2.0 and 4.0 parts by weight. If it is less than 2.0 parts by weight, the constructed three-dimensional spatial network will lack sufficient strength, failing to effectively suspend the high-density weighting agent and encapsulate the peeled oil droplets at high temperatures. If it is more than 4.0 parts by weight, the initial apparent viscosity of the system at room temperature will be too high, significantly increasing pumping friction and circulating equivalent density, which is detrimental to high-volume construction. In the above ratio of alkyl glycoside and alkyl sulfobetaine, the nonionic alkyl glycoside undertakes the main wetting and penetration function, while the alkyl sulfobetaine provides strong emulsification, dispersion, and oil film peeling capabilities at a lower dosage. The dosage range of the weighting agent covers the formation pressure requirements of different sections of ultra-deep wells: when the weighting agent dosage is in the lower range of 50 to 90 parts by weight, the fluid density of the isolation fluid is about 1.30 g / cm³ to 1.55 g / cm³, which is suitable for specific well sections with low formation pressure coefficients; while when the weighting agent dosage reaches about 100 parts by weight or more, with the selection of barite powder or hematite powder, the fluid density can be adjusted to the range of 1.6 g / cm³ to 2.4 g / cm³ usually required for high-pressure sections of ultra-deep wells.

[0007] More preferably, the isolation liquid further includes an antifoaming agent, and the amount of the antifoaming agent is 0.1 to 0.3 parts by weight per 100 parts by weight of the water, wherein the antifoaming agent is selected from silicone polyether modified antifoaming agents.

[0008] Furthermore, in the zwitterionic nanocomposite polymer, the effective components of 2-acrylamido-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride, isopentenyl polyoxyethylene ether, and surface silanized modified nano silica are fed in a mass ratio of (30 to 33):(40 to 45):(14 to 16):(5 to 7):(8 to 10):(2 to 4). Surface-silanized modified nano-silica accounts for only 2 to 4 parts of the total feed. Although individual nanoparticles carry a large number of methacryloyloxy double bonds after silanization grafting, during the copolymerization process, the pre-initiated segments, after growing on the nanoparticle surface, will form steric hindrance shielding on adjacent double bonds, making the actual number of effective double bonds participating in the copolymerization reaction significantly lower than the theoretical total number of grafts. In addition, the nanoparticles are highly diluted in the reaction system, and the average distance between particles is much larger than the radius of gyration of the polymer chain segments. A large number of chain segments exist in the form of overhanging arms connected only to individual nanoparticles, resulting in a limited effective interparticle bridging crosslinking density. This topology allows the polymer to undergo extreme swelling in water, driven by the huge osmotic pressure generated by the high density of ionic groups on the chain segments, even after drying. Ultimately, it is uniformly dispersed in the aqueous phase as a highly swollen microgel dispersion.

[0009] More preferably, the surface-silanized modified nano-silica is prepared by dehydration condensation reaction of γ-(methacryloyloxy)propyltrimethoxysilane with hydrophilic nano-silica with a native particle size of 15 nm to 25 nm and a specific surface area of ​​180 m² / g to 220 m² / g.

[0010] According to a specific embodiment of the present invention, the weighting agent is selected from at least one of barite powder or hematite powder. Preferably, the pH value of the broad-spectrum anti-fouling isolation liquid is 8.5 to 9.5, and the fluid density is 1.6 g / cm³ to 2.4 g / cm³.

[0011] According to another aspect of the present invention, a method for preparing the above-mentioned broad-spectrum anti-fouling isolation liquid is provided, comprising the following steps: Step (1) Preparing surface-silanized modified nano-silica: A surface grafting reaction is performed on hydrophilic nano-silica using γ-(methacryloyloxy)propyltrimethoxysilane to obtain the surface-silanized modified nano-silica. Step (2) Synthesizing zwitterionic nanocomposite polymer: In an aqueous system, using the surface-silanized modified nano-silica as a reaction anchor, N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride, and isopentenyl alcohol polyoxyethylene ether are added, and an in-situ free radical copolymerization reaction is carried out under the action of a composite initiation system. After separation and purification, the zwitterionic nanocomposite polymer is obtained. Step (3) Preparation of isolation liquid: The zwitterionic nanocomposite polymer is added to water and hydrated and swollen under shear stirring to form a base slurry; a composite rinsing agent containing alkyl glycosides and alkyl sulfobetaine surfactants is added to the base slurry, and then a weighting agent is added to adjust the system density to obtain the broad-spectrum anti-pollution isolation liquid.

[0012] Preferably, in step (1), the surface grafting reaction process includes: slowly adding γ-(methacryloyloxy)propyltrimethoxysilane to an acidic mixed solvent composed of ethanol and water for hydrolysis activation; then adding hydrophilic nano-silica, dispersing it ultrasonically, and stirring at 70°C for 2 hours; after the reaction, obtaining the surface silanized modified nano-silica by washing and extraction, centrifugation for solid-liquid separation, and vacuum drying; wherein, the pH value of the acidic mixed solvent is adjusted to 4.0; and the mass ratio of γ-(methacryloyloxy)propyltrimethoxysilane to the hydrophilic nano-silica is 2:1.

[0013] Further, in step (2), before adding the composite initiation system to carry out the polymerization reaction, an alkaline solution is added dropwise to the mixed suspension of each polymer monomer and inorganic crosslinking core, the pH value of the system is precisely adjusted to 7.0±0.1, and nitrogen gas is continuously bubbled to remove oxygen and degas for at least 30 minutes.

[0014] More preferably, in step (2), the composite initiation system is a redox-free radical composite initiation system, composed of ammonium persulfate, sodium bisulfite, and 2,2'-azobisisobutyramidine dihydrochloride, and the total amount of the composite initiation system accounts for 0.65 wt% of the total mass of all monomers. Preferably, the thermodynamic control conditions for the in-situ free radical copolymerization reaction are: the reaction initiation temperature is 55°C, the peak temperature during the exothermic polymerization is controlled within the range of 60°C to 65°C, and the reaction is carried out at a constant temperature for 4 to 5 hours within this range until the system is transformed into a highly elastic gel block.

[0015] More preferably, in step (2), the separation and purification process includes: cutting the highly elastic gel block obtained at the reaction endpoint into small pieces, then soaking it in a mixed polar solvent composed of anhydrous ethanol and acetone in a volume ratio of 1:1 for 24 hours for extraction, dehydration and precipitation washing; finally, drying the precipitate under vacuum at 65°C to constant weight and pulverizing it to obtain the zwitterionic nanocomposite polymer in powder form.

[0016] According to the specific implementation steps of the preparation method of the present invention, step (3) includes: slowly adding the zwitterionic nanocomposite polymer to the water under high-speed shear stirring at 3000 rpm, continuously stirring and allowing it to stand at room temperature for 24 hours for hydration and curing, so that the polymer particles are fully swollen and dispersed to form an aqueous slurry; adding the composite flushing agent and the silicone polyether modified defoamer to the aqueous slurry, and continuously shearing and mixing at 1000 rpm for 15 minutes; slowly adding the weighting agent at 1500 rpm, and continuously stirring until the barite or hematite particles are completely wrapped and dispersed by the polymer network to obtain the broad-spectrum anti-pollution isolation liquid.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves the following outstanding technical effects through the control of polymer chain segment topology and the thermodynamic reconstruction of the solid-liquid interface: The isolating liquid system of this invention completely overcomes the problem of polymer "thermodynamic dethickening" leading to the collapse of rheological and suspension capabilities under extremely high temperature and high salt conditions. Due to the introduction of a modified nano-silica rigid core and isopentenyl alcohol polyoxyethylene ether temperature-sensitive associated long chains, when the temperature is raised to high temperatures, the polyoxyethylene segments on the polymer side chains dehydrate due to the disruption of hydrogen bonds after exceeding their cloud point temperature. The dehydrated segments then undergo intermolecular association and physical cross-linking. This "temperature-sensitive continuous thickening" effect effectively counteracts the intrinsic high-temperature thermal degradation effect of the polymer, allowing the yield value of the isolating liquid to maintain a stable network strength at high temperatures, achieving excellent weighting agent suspension stability.

[0018] This invention significantly enhances the broad-spectrum anti-fouling capability of high-concentration oil-based drilling fluids and achieves complete wetting reversal at ultra-high temperatures. The amphoteric structure constructed by the sulfonic acid anionic sites and quaternary ammonium salt cation sites on the polymer chain makes the polymer as a whole near-neutral charge, greatly reducing its tendency to complex and precipitate with exogenous anionic emulsifiers. In the composite flushing agent, the alkyl glycoside, as a non-ionic component, maintains chemical stability at high temperatures and provides wetting and penetration capabilities. The zwitterionic head group of alkyl sulfobetaine prevents the formation of insoluble precipitates in the calcium and magnesium ion-rich environment of cementing operations. Furthermore, its molecule does not contain easily hydrolyzed functional groups such as ester or amide bonds, and the bond energy between the carbon-sulfur bond and the quaternary ammonium nitrogen is extremely high, maintaining an intact molecular structure and interfacial activity even at 240°C. The two work synergistically to effectively wedge into and peel off the dense oil film on the casing surface, encapsulating it to form a water-in-oil nanoemulsion with extremely small particle size, thus completely reversing the interface from a strongly oleophilic state to an extremely hydrophilic state. Detailed Implementation

[0019] The following detailed description of the broad-spectrum anti-fouling isolation fluid for ultra-deep well cementing and its preparation method, with reference to specific embodiments, is provided. However, the scope of protection of this invention is not limited to the following embodiments.

[0020] The isolation liquid system of this invention is assembled from zwitterionic nanocomposite polymers, composite flushing agents, weighting agents, defoamers, and water in a specific ratio. Its core lies in the chemical synthesis route of the zwitterionic nanocomposite polymer. The polymer is constructed using surface-silanized modified nano-silica as an inorganic crosslinking core, with methacryloyloxy double bonds introduced by a silane coupling agent serving as molecular grafting anchors. Polymer segments are directionally grown on the surface of the inorganic core through in-situ free radical copolymerization in an aqueous phase, ultimately forming a star-shaped organic-inorganic hybrid copolymer with nanoparticles as the central node and radiating multi-arm branches. It should be noted that although the surface of a single nano-silica particle carries a large number of methacryloyloxy double bonds after silanization grafting, a significant self-limiting effect exists in the actual copolymerization process: the first segment to grow on the nanoparticle surface creates steric hindrance shielding on adjacent surface double bonds, significantly reducing the reactivity of subsequent double bonds. The actual number of effective double bonds participating in copolymerization is significantly lower than the theoretical total number of grafted bonds. Furthermore, since nanoparticles account for only 2% to 4% of the total feed in the reaction system, the average distance between particles is much larger than the radius of gyration of polymer chain segments. A large number of chain segments exist as overhanging arms connected only to individual nanoparticles, thus limiting the effective interparticle bridging crosslinking density. This topology results in a large effective network grid size despite the polymer exhibiting a macroscopic gel state at the reaction endpoint. In water, the enormous ion osmotic pressure driven by the high-density distribution of sulfonic acid and quaternary ammonium groups on the chain segments forces the network to swell dramatically, ultimately resulting in a highly swollen microgel dispersion uniformly dispersed in the aqueous phase. Its rheological behavior is equivalent to that of a concentrated polymer solution, possessing sufficient continuous phase viscoelasticity to achieve the functions of weighting agent suspension and oil droplet encapsulation. In the polymer chain segment, 2-acrylamido-2-methylpropanesulfonic acid contributes fully ionized sulfonic acid anion sites to construct an electrostatic repulsion layer and shield against double-layer compression damage from polyvalent cations; the tertiary amide bond provided by N,N-dimethylacrylamide, lacking an active hydrogen atom on the α-carbon, can circumvent high-temperature hydrolytic chain scission caused by the imine alcohol tautomerization pathway; the five-membered lactam ring of N-vinylpyrrolidone increases the rotational barrier of local segments of the main chain, enhancing segment rigidity; and dimethyl diallyl ammonium chloride introduces a quaternary ammonium salt cation. The isopentenyl alcohol polyoxyethylene ether (IPOE) forms an amphoteric charge balance with the sulfonic acid group at the subsite site. As a thermosensitive macromolecular associating monomer, the main polyoxyethylene chain segment maintains a hydrophilic hydration shell at room temperature through hydrogen bonds between the ether oxygen atoms and water molecules. When the ambient temperature rises above the cloud point temperature of this polyoxyethylene chain segment, the hydrogen bonds are broken extensively by intense thermal motion. After dehydration, the chain segment associates with other molecules to reduce the system's free energy, constructing a dynamically reversible physical cross-linked network to compensate for the thickening effect caused by the intrinsic thermal degradation of the main chain. This association mechanism differs from the classic long-chain alkyl hydrophobic association; its essence is the thermally induced dehydration and aggregation of the polyoxyethylene chain segment, which belongs to the cloud point behavior of polyether polymers in polymer physics.The composite flushing agent is a combination of alkyl glycosides and alkyl sulfobetaine. The former is a nonionic glycoside surfactant, which has excellent heat resistance and washing properties because its sugar ring skeleton is not easily dehydrated and decomposed above 200℃. The latter is an amphoteric surfactant, which contains only two functional groups, quaternary ammonium nitrogen and sulfonate, connected by carbon-nitrogen bonds and carbon-sulfur bonds. It does not contain ester bonds, amide bonds, or ether bonds, which are easily hydrolyzed under alkaline and high-temperature conditions. Therefore, it maintains its complete molecular structure and interfacial activity even under extreme conditions of 240℃ and pH 9.5. Its amphoteric head group structure prevents the formation of insoluble calcium soap precipitates in the calcium and magnesium ion-rich environment of cementing operations, unlike anionic surfactants, thus ensuring the continuous effectiveness of oil film stripping function across the entire well depth range.

[0021] The raw materials and their specifications required for synthesis and preparation are as follows: Hydrophilic nano-silica was prepared using Aerosil 200 fumed silica from Degussa, with a native particle size of 15 nm to 25 nm, a specific surface area of ​​200 ± 20 m² / g, and a purity of not less than 99.8%. It was vacuum-dried at 120℃ for 4 hours before use to remove physically adsorbed water. γ-(methacryloyloxy)propyltrimethoxysilane was purchased from Nanjing Shuguang Chemical Group, with a purity of not less than 98.0%. 2-Acrylamido-2-methylpropanesulfonic acid was a polymerization-grade crystalline powder provided by Shouguang Weidong Chemical. N,N-Dimethylacrylamide was purchased from Shanghai Aladdin Reagent, with a purity of not less than 99.5%. Before use, it was purified by passing the polymerization inhibitor through a chromatography column packed with neutral alumina. N-Vinylpyrrolidone was a polymerization-grade liquid monomer from Ashland Corporation, USA. Dimethyl diallyl ammonium chloride was a 60% aqueous solution provided by Shandong Nuoer Biotechnology. The isopentenyl alcohol polyoxyethylene ether used was TPEG-2400 produced by Liaoning Kelong Fine Chemical Co., Ltd., with a weight average molecular weight of approximately 2400. Ammonium persulfate and sodium bisulfite were analytical grade and provided by Sinopharm Group; 2,2′-azobisisobutyramidine dihydrochloride was V-50 from Wako Pure Chemical Industries, Ltd., Japan. The alkyl glycoside used was APG-0810, with a solid content of 50% and a carbon chain distribution of C8 to C10. The alkyl sulfobetaine surfactant used was tetradecyl dimethyl sulfopropyl betaine (SB-14), provided by Shanghai Maclean Biochemical Technology Co., Ltd., with a purity of not less than 99%. The chemical structure of this compound is that a tetradecyl group is directly linked to a dimethyl quaternary ammonium nitrogen group via a carbon-nitrogen bond, and the quaternary ammonium nitrogen group is then linked to a sulfonate group via a propyl carbon chain; the molecule does not contain any ester or amide bonds. The barite powder is drilling grade, with a density of 4.2 g / cm³, and passes through a 325-mesh standard sieve; the hematite powder has a density of 5.05 g / cm³, and also passes through a 325-mesh sieve. The silicone-based polyether modified defoamer used is Wacker Chemie H10 from Germany.

[0022] The specific preparation process of surface-silanized modified nano-silica is as follows. In a 500 mL three-necked flask equipped with a mechanical stirrer, condenser, and temperature probe, 200 mL of a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 1:1 was added. The stirring speed was turned on at 400 r / min, and the pH of the system was adjusted to 4.0 by titration with 0.1 mol / L glacial acetic acid. 10.0 g of γ-(methacryloyloxy)propyltrimethoxysilane was weighed and slowly added dropwise to the solvent, and the solution was hydrolyzed and activated in a 30℃ water bath for 30 min until the solution became clear. Subsequently, 5.0 g of hydrophilic nano-silica, which had been pre-dried under vacuum at 120℃ for 4 hours, was added in batches to the hydrolysate, maintaining a silane coupling agent to nano-silica mass ratio of 2:1. The mixture was ultrasonically dispersed for 20 min using a 400 W ultrasonic cell disruptor. The system was then transferred to a 70℃ oil bath and heated, with the stirring speed adjusted to 600 r / min, and the reaction was carried out at a constant temperature for 2 hours. After the reaction, the suspension was transferred to a high-speed centrifuge and centrifuged at 8000 r / min for 10 min to separate the solids. The precipitate was redispersed with anhydrous ethanol and ultrasonically washed and centrifuged three times to completely remove free silanes and their oligomers. The resulting filter cake was dried in a vacuum oven at 60℃ for 12 hours, ground, and passed through a 100-mesh sieve to obtain surface-silanized modified nano-silica, denoted as . .

[0023] The synthesis process of the zwitterionic nanocomposite polymer is as follows: 400 g of ultrapure deionized water was added to a 1000 mL glass reactor equipped with an anchor-type stirrer, a nitrogen conduit, a dual-channel constant-pressure dropping funnel, and a PID temperature control jacket. The stirring speed was turned on at 300 r / min. 2-Acrylamido-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride aqueous solution, isopentenyl alcohol polyoxyethylene ether, and other components were added sequentially according to the predetermined feed ratio. Powder. While cooling with an ice-water bath, slowly add a 10 mol / L sodium hydroxide aqueous solution, and precisely adjust the pH of the system to 7.0±0.1 using a precision pH meter for online monitoring. After pH adjustment, insert a nitrogen gas delivery tube deep below the liquid surface at the bottom of the reactor and continuously bubble at a flow rate of 200 mL / min for 30 min to remove dissolved oxygen. In the last 10 minutes of deoxygenation, connect the reactor jacket to a 55℃ constant-temperature circulating water system to allow the system temperature to rise steadily to the reaction initiation temperature of 55℃. Under nitrogen protection, prepare three sets of initiators as dilute solutions and slowly and uniformly add them to the reactor over 15 min using a dropping funnel in a semi-continuous manner. Because the initiators are added slowly in stages rather than all at once, the instantaneous free radical concentration in the reactor is extremely low, and the reaction starts gradually at a moderate rate. After the initiators are added, immediately switch the circulating water in the jacket to 15℃ cooling water, seal the reactor, reduce the stirring speed to 150 r / min, and enter the chain growth temperature control stage. Chain growth is an exothermic process. During this process, a heat transfer temperature difference of 45 to 50°C exists between the jacket cooling water temperature (15°C) and the target temperature inside the reactor (60 to 65°C). Even under conditions where the heat transfer coefficient of the glass reactor is relatively low, this difference is sufficient to provide adequate heat flux to remove the exothermic polymerization. Simultaneously, the solid content of this system is approximately 20%, and the large amount of water effectively buffers the heat release during polymerization. The cooling water flow rate is adjusted in real-time using a PID temperature control system to stably maintain the reactor temperature within the 60°C to 65°C range. The reaction is carried out at this constant temperature for 4 to 5 hours, until the system completely loses its macroscopic fluidity, transforms into a highly elastic gel block, and the stirring torque reaches its peak and remains stable for 30 minutes, at which point the reaction is stopped. The gel block was completely removed from the autoclave and mechanically granulated to 2-3 mm particles. The particles were then immersed in 1500 mL of a mixed polar solvent of anhydrous ethanol and acetone in a 1:1 volume ratio and extracted at room temperature for 24 hours, with the solvent replaced once during the extraction to thoroughly extract residual monomers and initiator residues. The resulting solid precipitate was transferred to a 65°C vacuum drying oven and dried to constant weight. After being pulverized by an ultra-fine high-speed pulverizer and passed through a 120-mesh sieve, a free-flowing, white to slightly yellow zwitterionic nanocomposite polymer, denoted as TNZP, was obtained.

[0024] The preparation process of the isolation fluid is as follows: Add 100 parts by weight of deionized water to a high-speed shear dispersion tank equipped with a frequency converter, adjust to a high-speed shear stirring state of 3000 r / min, and slowly and evenly sprinkle TNZP dry powder into the center of the vortex, controlling the feeding time to 15 min to avoid the formation of localized water-encapsulated fish-eye-like clumps; after the feeding is complete, stir continuously at room temperature for 2 hours, and then allow to stand for hydration and curing for 24 hours to allow the polymer network to fully swell and disperse under ion osmotic pressure to form a uniform aqueous slurry. Reduce the stirring speed to 1000 r / min, and add alkyl glycoside, tetradecyl dimethyl sulfopropyl betaine, and silicone polyether modified defoamer in sequence, continuously shearing and mixing for 15 min. Finally, adjust the stirring speed to 1500 r / min, and slowly add the weighting agent through the screw feeder. After the addition is complete, continue stirring for 30 min until the barite or hematite particles are completely and uniformly coated and dispersed by the polymer network. If necessary, use diluted ammonia or sodium carbonate solution to fine-tune the pH of the system to between 8.5 and 9.5 to obtain the target broad-spectrum anti-pollution isolation liquid.

[0025] To objectively evaluate the products of each embodiment and comparative example, the key engineering performance indicators of the isolation fluid were tested using the following standard methods. Rheological properties were measured at 25°C using a Fann 35SA six-speed rotational viscometer, according to the methods specified in GB / T 16783.1-2014, determining the apparent viscosity, plastic viscosity, and yield value at room temperature. High-temperature and high-pressure aging tests were performed according to GB / T 29170-2012, with rolling aging at 220°C and 10 MPa for 16 h, and at 240°C and 15 MPa for 72 h. After aging, the rheological parameters were remeasured after cooling to room temperature. Fluid density was measured using a metal cup densitometer as specified in GB / T 16783.1. Sedimentation stability was characterized by the sedimentation factor. The aged sample was weighed in two sections according to the method in SY / T 5119, and the sedimentation factor was calculated using the formula. The ideal homogeneous state was 0.500. Wetting reversal performance was assessed using a German KRÜSSDSA100 contact angle meter. The contact angle between the isolating fluid and a metal substrate pre-coated with simulated oil-based drilling cake was measured over time on a 220°C high-temperature sample stage. The contact angle value was recorded after 5 minutes of contact. Cake flushing displacement efficiency was determined according to API RP 10B-2. After flushing at a set flow rate for 5 minutes, the percentage of oil film stripped from the initial oil film was calculated using the weight loss method. Anti-fouling ability was characterized by slurry stability. The example sample was mixed with a typical oil-based drilling fluid at a volume ratio of 7:3. After rolling aging at 220°C and 10 MPa for 16 hours, the apparent viscosity was measured and compared with that before mixing, and the viscosity fluctuation rate was calculated. pH values ​​were directly read at room temperature using a Shanghai Leici PHS-3C pH meter. Example 1

[0026] Will The preparation of TNZP and its synthesis were performed according to the above process. The mass of each raw material fed in the synthesis of TNZP was as follows: 31.4 g of 2-acrylamido-2-methylpropanesulfonic acid, 42.3 g of N,N-dimethylacrylamide, 15.0 g of N-vinylpyrrolidone, 10.0 g of 60% aqueous solution of dimethyl diallyl ammonium chloride (equivalent to 6.0 g of effective substance), and 9.0 g of isopentenyl alcohol polyoxyethylene ether. 3.0 g, corresponding to a mass ratio of 31.4:42.3:15.0:6.0:9.0:3.0 for the six components, with a total mass of 103.7 g for the five organic monomers. The total amount of composite initiator was 0.67 g (approximately 0.65 wt% of the total organic monomer mass), including 0.26 g of ammonium persulfate, 0.25 g of sodium bisulfite, and 0.16 g of 2,2′-azobisisobutyramidine dihydrochloride. The reaction was started at 55°C, and after the initiator was added, the temperature was switched to 15°C for cooling water control, and the reaction was carried out at a constant temperature of 60°C to 63°C for 4.5 h. When preparing the isolation solution, based on 100 parts by weight of deionized water, add 3.0 parts of TNZP, 2.0 parts of alkyl glycoside, 0.5 parts of tetradecyl dimethyl sulfopropyl betaine, 0.2 parts of silicone polyether modified defoamer, and 220 parts of barite powder in sequence. Finally, adjust the pH of the system to 9.0, and the density of the resulting isolation solution is 2.06 g / cm³. Example 2

[0027] The feedstocks used in the synthesis of TNZP were as follows: 30.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 40.0 g of N,N-dimethylacrylamide, 14.0 g of N-vinylpyrrolidone, 8.33 g of a 60% aqueous solution of dimethyl diallyl ammonium chloride (equivalent to 5.0 g of effective substance), and 8.0 g of isopentenyl alcohol polyoxyethylene ether. 2.0 g of the feed material was used, corresponding to a feed ratio of 30:40:14:5:8:2 as defined in the claims of this invention. The reaction conditions were the same as in Example 1, with a peak temperature of 60°C and a constant temperature reaction time of 5 h. When preparing the isolation solution, based on 100 parts by weight of deionized water, 2.0 parts of TNZP, 1.5 parts of alkyl glycoside, 0.3 parts of tetradecyl dimethyl sulfopropyl betaine, 0.1 parts of defoamer, and 100 parts of barite powder were added to adjust the pH of the system to 8.5. The resulting isolation solution had a density of 1.60 g / cm³. Example 3

[0028] The feedstock quantities for TNZP synthesis are as follows: 33.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 45.0 g of N,N-dimethylacrylamide, 16.0 g of N-vinylpyrrolidone, 11.67 g of a 60% aqueous solution of dimethyl diallyl ammonium chloride (equivalent to 7.0 g of effective substance), and 10.0 g of isopentenyl alcohol polyoxyethylene ether. 4.0 g, corresponding to a feed mass ratio of 33:45:16:7:10:4 (upper limit of claims). When preparing the isolation solution, based on 100 parts by weight of deionized water, add 4.0 parts TNZP, 2.5 parts alkyl glycoside, 0.8 parts tetradecyl dimethyl sulfopropyl betaine, 0.3 parts defoamer, and 280 parts hematite powder as a weighting agent. Adjust the pH of the system to 9.5. The resulting isolation solution has a density of 2.38 g / cm³. Example 4

[0029] The synthesis scheme of TNZP is exactly the same as that in Example 1. When preparing the isolation solution, based on 100 parts by weight of deionized water, add 3.0 parts of TNZP, 2.0 parts of alkyl glycoside, 0.5 parts of tetradecyl dimethyl sulfopropyl betaine, and 0.2 parts of defoamer. Replace the weighting agent with 200 parts of hematite powder, adjust the pH of the system to 9.0, and the density of the resulting isolation solution is 2.11 g / cm³. Example 5

[0030] The feedstock quantities for TNZP synthesis were as follows: 32.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 43.5 g of N,N-dimethylacrylamide, 15.5 g of N-vinylpyrrolidone, 10.83 g of a 60% aqueous solution of dimethyl diallyl ammonium chloride (equivalent to 6.5 g of effective substance), and 9.5 g of isopentenyl alcohol polyoxyethylene ether. 3.5 g corresponds to a feed mass ratio of 32:43.5:15.5:6.5:9.5:3.5. When preparing the isolation solution, based on 100 parts by weight of deionized water, add 3.5 parts TNZP, 2.2 parts alkyl glycoside, 0.6 parts tetradecyl dimethyl sulfopropyl betaine, 0.25 parts defoamer, and 275 parts barite powder. Adjust the pH of the system to 9.2. The resulting isolation solution has a density of 2.22 g / cm³. Example 6

[0031] The feedstock quantities for TNZP synthesis are as follows: 30.5 g of 2-acrylamido-2-methylpropanesulfonic acid, 41.0 g of N,N-dimethylacrylamide, 14.5 g of N-vinylpyrrolidone, 9.17 g of a 60% aqueous solution of dimethyl diallyl ammonium chloride (equivalent to 5.5 g of effective substance), and 8.5 g of isopentenyl alcohol polyoxyethylene ether. 2.5 g corresponds to a feed mass ratio of 30.5:41.0:14.5:5.5:8.5:2.5. When preparing the isolation solution, based on 100 parts by weight of deionized water, add 2.5 parts TNZP, 1.8 parts alkyl glycoside, 0.4 parts tetradecyl dimethyl sulfopropyl betaine, 0.15 parts defoamer, and 160 parts barite powder, adjust the pH of the system to 8.8, and the resulting isolation solution has a density of 1.86 g / cm³.

[0032] Comparative Example 1 During the synthesis of TNZP, isopentenyl alcohol polyoxyethylene ether monomer was completely removed. The types of other raw materials, feeding ratios, composite initiation systems, and polymerization process conditions were all consistent with those in Example 1. The resulting polymer was designated as TNZP-N1. The preparation process of the isolation solution and the dosage of each auxiliary material were completely consistent with those in Example 1. The weighting agent was 220 parts of barite powder with a density of 2.06 g / cm³.

[0033] Comparative Example 2 The zwitterionic nanocomposite polymer of this invention is completely abandoned, and instead, industrially commonly used high molecular weight partially hydrolyzed polyacrylamide (molecular weight of about 15 million, degree of hydrolysis of 22%, purchased from Beijing Hengju Chemical) is used to replace TNZP in the same mass parts; the remaining formulation components and preparation process are completely consistent with Example 1, and the weighting agent is 220 parts of barite powder with a density of 2.06 g / cm³.

[0034] Comparative Example 3 Complete removal during TNZP synthesis The inorganic crosslinking core was used for homogeneous aqueous solution polymerization with only five monomers under the same composite initiation system. The proportions of other monomers and the process conditions were the same as in Example 1. The resulting pure organic amphoteric polymer was designated TNZP-N3. The preparation process of the isolation solution and the dosage of each auxiliary material were consistent with those in Example 1. The weighting agent was 220 parts of barite powder with a density of 2.06 g / cm³.

[0035] Comparative Example 4 The synthesis and dosage of TNZP were exactly the same as in Example 1. In the composite flushing agent, alkyl glycosides and tetradecyl dimethyl sulfopropyl betaine were replaced with the traditional anionic-nonionic compound combination of sodium dodecylbenzenesulfonate (2.0 parts) and OP-10 (0.5 parts), which are commonly used on site. The dosage and preparation process of other components remained unchanged. The weighting agent was 220 parts of barite powder with a density of 2.06 g / cm³.

[0036] The isolation fluid samples obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were systematically tested according to the aforementioned standard methods, and the data obtained are summarized in the table below.

[0037] Sample number System density (g·cm⁻³) Apparent viscosity at room temperature (mPa·s) Apparent viscosity (mPa·s) after rolling aging at 220℃ for 16 h Yield value / Pa after rolling aging at 240℃ for 72 h Sedimentation factors after high temperature aging Contact angle / ° after 5 min of contact angle reversal at 220℃ Filter cake flushing displacement efficiency / % Viscosity fluctuation rate after mixing with 30% oil-based mud / % Example 1 2.06 45 58 13.8 0.510 <10 98.8 11.5 Example 2 1.60 38 51 12.4 0.516 12 96.3 14.2 Example 3 2.38 64 78 16.8 0.506 <10 99.2 9.5 Example 4 2.11 47 60 14.0 0.511 <10 98.5 11.8 Example 5 2.22 50 64 14.6 0.509 <10 98.7 10.6 Example 6 1.86 42 54 13.0 0.514 11 97.5 12.7 Comparative Example 1 2.06 40 22 5.2 0.628 26 81.4 36.5 Comparative Example 2 2.06 68 14 1.8 0.792 88 53.6 The system became gelatinized and could not be measured. Comparative Example 3 2.06 33 29 8.4 0.567 22 86.7 23.4 Comparative Example 4 2.06 46 55 13.0 0.522 67 70.2 44.1 As can be seen from the data in the table above, the samples in Examples 1 to 6 are significantly superior to the comparative examples in key indicators such as apparent viscosity at room temperature, rheological retention rate after high-temperature aging, weighting agent suspension stability, ultra-high temperature wetting reversal efficiency, and resistance to oil-based drilling fluid contamination. Example 3 uses the upper limit of the dosage of each component and high-density hematite powder as the weighting agent, with a density of 2.38 g / cm³. Although the viscosity at room temperature reaches 64 mPa·s, it is still within the range that can be pumped on site. The yield value reaches 16.8 Pa after rolling aging at 240℃ for 72 h, and the sedimentation factor is as low as 0.506, which reflects the ultimate bearing capacity of the grid strength under high-density load. In contrast, Example 2 uses the lower limit of both the dosage of each component and the feeding ratio. With 100 parts of barite powder, the system density is 1.60 g / cm³. It still meets the qualified level in terms of sedimentation factor, flushing efficiency, and contact angle reversal, indicating that the formulation of the present invention has good engineering robustness in a wide range of densities. Examples 5 and 6 exhibit a clear parameter gradient transition characteristic compared to Example 1. With the simultaneous increase in TNZP dosage and isopentenyl alcohol polyoxyethylene ether ratio, the high-temperature yield value and rinsing efficiency of the system show a steady upward trend, while the sedimentation factor shows a downward trend. This is consistent with the chemical logic that the increased polyoxyethylene chain content leads to an increase in high-temperature dehydration association nodes. In Example 4, when hematite powder was used instead of barite powder, the room-temperature viscosity increased slightly, while the sedimentation factor and rinsing efficiency remained basically the same as in Example 1, confirming that the system of the present invention has good coating stability for different types of weighting agents.

[0038] In Comparative Example 1, after removing isopentenyl alcohol polyoxyethylene ether, the viscosity of the system plummeted to 22 mPa·s after aging at 220℃, and the yield value was only 5.2 Pa after aging at 240℃ for 72 h. The sedimentation factor soared to 0.628, demonstrating the irreplaceable role of this temperature-sensitive associating monomer in resisting high-temperature thermal degradation and thickening. Comparative Example 2 used conventional partially hydrolyzed polyacrylamide. The easily hydrolyzed primary amide groups on its main chain underwent severe amide-carboxylic acid hydrolysis and chain scission at 240℃. Coupled with the lack of amphoteric charge balance, it immediately formed irreversible flocculation by polyelectrolyte-surfactant complexation upon encountering anionic emulsifiers in oil-based drilling fluids, resulting in a sedimentation factor as high as 0.792. This fully exposed the multiple failures of conventional linear thickeners under extreme conditions. Comparative Example 3 removed... After the inorganic crosslinking core, the resulting pure organic polymer exists in true solution form without crosslinking nodes. After aging, its yield value is only 8.4 Pa, and its sedimentation factor is 0.567. Its performance is between that of Example 1 and Comparative Example 1, confirming that the nano-rigid core and the temperature-sensitive associated long chain have a synergistic effect in network construction and are indispensable. In Comparative Example 4, after replacing the alkyl glycoside and sulfobetaine compound flushing agent of the present invention with the conventional combination of sodium dodecylbenzenesulfonate and OP-10, although sodium dodecylbenzenesulfonate itself has excellent high-temperature thermal stability, as an anionic surfactant, it underwent a strong electrostatic complexation reaction with the cationic quaternary ammonium salt sites on the chain in the zwitterionic polymer system of the present invention, generating a water-insoluble polyelectrolyte-surfactant complex precipitate, leading to a significant decrease in the effective free surfactant concentration in the system. Furthermore, the anionic sulfonate surfactant will further fail in cementing operations in environments rich in calcium and magnesium ions due to the bridging and flocculation effect of polyvalent cations. The aforementioned dual factors combined to result in incomplete contact angle reversal (67°), low rinsing efficiency (70.2%), and severe fluctuations in slurry viscosity (44.1%) in Comparative Example 4. This comparative data profoundly reveals the necessity of selecting alkyl sulfobetaine, an amphoteric rinsing agent, for molecular-level compatibility design with the amphoteric polymer in this invention: the amphoteric surfactant does not undergo stoichiometric complexation with anionic or cationic sites on the polymer chain, and its near-neutral charge characteristic of its amphoteric head groups naturally resists precipitation failure caused by calcium and magnesium ions, thus maintaining highly efficient interfacial activity under all operating conditions.

[0039] From a microscopic chemical mechanism perspective, the superior overall performance demonstrated in the examples stems from the coupling effect of a multi-level synergistic mechanism. At the polymer network level, surface-silanized modified nano-silica acts as the core node of the multi-armed star-shaped macromolecule in the copolymerization system, and the methacryloyloxy double bonds on its surface initiate chain growth during the polymerization reaction. As mentioned earlier, due to the spatial shielding effect of chain segment growth on adjacent surface double bonds and the high dilution of nanoparticles in the system, the polymer forms a wide network with a limited effective crosslinking density. This network exhibits a gel morphology in the dry state, but undergoes extreme swelling in water due to the enormous Donnan osmotic pressure driven by the high density of sulfonic acid groups (fully ionized) and quaternary ammonium salt groups on the chain segments—the principle is consistent with the swelling mechanism of superabsorbent polymers, except that this system has a larger equilibrium swelling ratio due to its extremely low effective crosslinking density. The fully swollen microgel dispersion is macroscopically rheologically equivalent to a concentrated polymer solution system. In the chain segments surrounding the crosslinking core, the tertiary amide contributed by N,N-dimethylacrylamide, due to the absence of an active hydrogen atom on the α-carbon, fundamentally avoids the high-temperature hydrolysis caused by the imine alcohol tautomerization pathway; the five-membered lactam ring of N-vinylpyrrolidone increases the rotational barrier of the adjacent carbon-carbon single bonds in the main chain, thereby enhancing the rigidity of the local chain segments; the sulfonic acid group provided by 2-acrylamido-2-methylpropanesulfonic acid is completely ionized under system pH conditions of 8.5 to 9.5, and the resulting high-density anionic layer resists the compression of the electric double layer by calcium and magnesium ions through electrostatic repulsion. Regarding the anti-flocculation mechanism of the system, this invention does not rely on a single factor, but rather reduces the tendency of the polymer to undergo irreversible complexation and precipitation with exogenous anionic emulsifiers through the synergistic effect of three levels: First, the quaternary ammonium salt cation sites introduced by dimethyl diallyl ammonium chloride and the sulfonic acid anionic sites introduced by 2-acrylamido-2-methylpropanesulfonic acid coexist on the same macromolecular chain, making the polymer as a whole a near-neutral charge state, which significantly reduces the thermodynamic driving force for forming stoichiometric ion pairing with anionic emulsifiers; Second, the mass percentage of dimethyl diallyl ammonium chloride in the copolymer is only 5% to 7%, and the cation sites are diluted and dispersed on the polymer chain by a high proportion of neutral monomers, making it difficult for emulsifier molecules to find sufficiently dense cation regions for multi-point synergistic adsorption; Third, the microgel structure restricts the conformational freedom of polymer chain segments, making them lack the chain segment flexibility of linear polyelectrolytes that can freely coil and wrap anionic micelles. The temperature-sensitive adaptive thickening effect originates from the thermoinduced phase behavior of the polyoxyethylene segments introduced by isopentenyl alcohol polyoxyethylene ether: at room temperature, the polyoxyethylene segments maintain a hydrophilic hydration shell through ether oxygen-water hydrogen bonds, the intermolecular forces are weak, and the system exhibits low viscosity and high fluidity; when the temperature rises above the cloud point, the hydrogen bond network is largely destroyed, the polyoxyethylene segments dehydrate and shrink, and the dehydrated segments cross the molecular boundary to form dynamic and reversible physical association nodes between microgel particles, which increases the equivalent hydrodynamic scale and effectively counteracts the thermal degradation and thickening induced by high temperature.At the surfactant level, the sugar ring structure of alkyl glycosides remains chemically stable above 220°C, providing wetting and penetration capabilities for high-temperature resistant nonionic flushing components. Tetradecyl dimethyl sulfopropyl betaine contains only two high-energy bond groups in its molecular structure: carbon-nitrogen bonds (quaternary ammonium bonds) and carbon-sulfur bonds (sulfonate groups). It lacks ester bonds, amide bonds, and other functional groups that are prone to hydrolysis under alkaline and high-temperature conditions. Therefore, it maintains molecular integrity and full interfacial activity even under extreme conditions of 240°C and pH 9.5. Its zwitterionic head group structure makes the molecule electrically neutral overall, preventing it from losing activity in cementing environments rich in calcium and magnesium ions, unlike anionic surfactants which may form insoluble salts (such as calcium soaps) with polyvalent cations. When encountering oil-based mud intrusion, alkyl glycosides and sulfobetaine preferentially wedge into the oil-metal interface due to their lower interfacial tension, curling and peeling the oil film into tiny oil droplets. These droplets are instantly encapsulated by a polymer microgel network and composite surfactants, forming an oil-in-water nanoemulsion. Protected by the steric hindrance of the zwitterionic polymer, they cannot re-aggregate or adsorb back onto the solid surface, thus achieving a complete wetting reversal from strong oleophilicity to strong hydrophilicity. This lays a clean interfacial foundation for the formation of a strong chemical bond between the hydrated calcium silicate gel and the casing and rock matrix during cement hydration. The multiple performance degradations exhibited in the comparative example further confirm the irreplaceable nature of each of the aforementioned molecular structural elements and formulation parameters.

[0040] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A broad-spectrum anti-fouling isolation fluid for cementing ultra-deep wells, characterized in that, It includes the following components: zwitterionic nanocomposite polymer, composite flushing agent, weighting agent, and water; The zwitterionic nanocomposite polymer is an organic-inorganic hybrid copolymer with surface-silanized modified nano-silica as an inorganic crosslinking core, and with polymeric segments copolymerized and grafted onto the surface of the inorganic crosslinking core; the polymeric monomers of the polymeric segments include N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride, and isopentenyl polyoxyethylene ether. The composite flushing agent contains alkyl glycosides and alkyl sulfobetaine surfactants.

2. The broad-spectrum anti-fouling isolation liquid according to claim 1, characterized in that, Based on 100 parts by weight of the water, the amounts of each component are as follows: 2.0 to 4.0 parts by weight of the zwitterionic nanocomposite polymer, 1.5 to 2.5 parts by weight of the alkyl glycoside, 0.3 to 0.8 parts by weight of the alkyl sulfobetaine surfactant, and 50 to 300 parts by weight of the weighting agent; preferably, the isolation liquid further includes an antifoaming agent, and based on 100 parts by weight of the water, the amount of the antifoaming agent is 0.1 to 0.3 parts by weight, and the antifoaming agent is selected from silicone polyether modified antifoaming agents.

3. The broad-spectrum anti-fouling isolation liquid according to claim 1 or 2, characterized in that, In the zwitterionic nanocomposite polymer, the effective components of 2-acrylamido-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride, isopentenyl polyoxyethylene ether, and surface-silanized modified nano-silica are fed in a mass ratio of (30 to 33): (40 to 45): (14 to 16): (5 to 7): (8 to 10): (2 to 4); the surface-silanized modified nano-silica is prepared by dehydration condensation reaction of γ-(methacryloyloxy)propyltrimethoxysilane and hydrophilic nano-silica with a primary particle size of 15 nm to 25 nm and a specific surface area of ​​180 m² / g to 220 m² / g.

4. The broad-spectrum anti-fouling isolation fluid according to claim 1, characterized in that, The weighting agent is selected from at least one of barite powder or hematite powder.

5. A method for preparing a broad-spectrum anti-fouling isolation fluid as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step (1) Preparation of surface-silanized modified nano-silica: Hydrophilic nano-silica is grafted onto the surface using γ-(methacryloyloxy)propyltrimethoxysilane to obtain the surface-silanized modified nano-silica. Step (2) Synthesis of zwitterionic nanocomposite polymer: In an aqueous system, using the surface-silanized modified nano-silica as the reaction anchor, N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride and isopentenyl polyoxyethylene ether are added. Under the action of the composite initiation system, an in-situ free radical copolymerization reaction is carried out. After separation and purification, the zwitterionic nanocomposite polymer is obtained. Step (3) Preparation of isolation liquid: The zwitterionic nanocomposite polymer is added to water and hydrated and swollen under shear stirring to form a base slurry; a composite rinsing agent containing alkyl glycosides and alkyl sulfobetaine surfactants is added to the base slurry, and then a weighting agent is added to adjust the system density to obtain the broad-spectrum anti-pollution isolation liquid.

6. The method according to claim 5, characterized in that, In step (1), the surface grafting reaction process includes: γ-(methacryloyloxy)propyltrimethoxysilane was slowly added dropwise to an acidic mixed solvent of ethanol and water for hydrolysis and activation; then hydrophilic nano-silica was added, and after ultrasonic dispersion, the mixture was stirred at 70°C for 2 hours; after the reaction was completed, the surface-silanized modified nano-silica was obtained by washing and extraction, centrifugation for solid-liquid separation, and vacuum drying. The pH value of the acidic mixed solvent is adjusted to 4.0; the mass ratio of γ-(methacryloyloxy)propyltrimethoxysilane to the hydrophilic nano silica is 2:

1.

7. The method according to claim 5, characterized in that, In step (2), before adding the composite initiation system to carry out the polymerization reaction, an alkaline solution is added dropwise to the mixed suspension of each polymer monomer and inorganic crosslinking core, the pH value of the system is precisely adjusted to 7.0±0.1, and nitrogen gas is continuously bubbled to remove oxygen and degas for at least 30 minutes.

8. The method according to claim 5, characterized in that, In step (2), the composite initiation system is a redox-free radical composite initiation system, composed of ammonium persulfate, sodium bisulfite and 2,2'-azobisisobutyramidine dihydrochloride, and the total amount of the composite initiation system accounts for 0.65 wt% of the total mass of all monomers; preferably, the thermodynamic control conditions of the in-situ free radical copolymerization reaction are: the reaction initiation temperature is 55℃, the peak temperature during the polymerization exothermic period is controlled in the range of 60℃ to 65℃, and the reaction is carried out at a constant temperature for 4 to 5 hours in this range until the system is transformed into a highly elastic gel block.

9. The method according to claim 5 or 8, characterized in that, In step (2), the separation and purification process includes: cutting the highly elastic gel block obtained at the reaction endpoint into small pieces, then soaking it in a mixed polar solvent composed of anhydrous ethanol and acetone in a volume ratio of 1:1 for 24 hours for extraction, dehydration and precipitation washing; finally, drying the precipitate under vacuum at 65°C to constant weight and pulverizing it to obtain the zwitterionic nanocomposite polymer in powder form.

10. The method according to claim 5, characterized in that, Step (3) includes the following process: The zwitterionic nanocomposite polymer was slowly added to the water under high-speed shear stirring at 3000 rpm, and the mixture was continuously stirred and allowed to stand at room temperature for 24 hours for hydration curing, so that the polymer particles could be fully swollen and dispersed to form an aqueous slurry. The composite rinsing agent and silicone polyether modified defoamer were added to the aqueous slurry, and the mixture was continuously sheared and mixed at 1000 rpm for 15 minutes. The weighting agent is slowly added at 1500 rpm, and the mixture is stirred continuously until the barite or hematite particles are completely encapsulated and dispersed by the polymer network to obtain the broad-spectrum anti-pollution isolation liquid.